Dimmers for controlling the amount of light emitted by a lighting load have been known in the art (see, for example, Patent Literature 1).
The dimmer disclosed in Patent Literature 1 includes a pair of terminals, a control circuit unit, a control power supply unit for supplying control power to the control circuit unit, and a lighting control operating unit for setting the lighting level of the lighting load.
Between the pair of terminals, connected in parallel are the control circuit unit and the control power supply unit. In addition, a series circuit of an AC power supply and the lighting load is also connected between the pair of terminals. The lighting load includes a plurality of light-emitting diodes (LEDs) and a power supply circuit for turning these LEDs ON. The power supply circuit includes a smoothing circuit including a diode and an electrolytic capacitor.
The control circuit unit includes a switch unit for performing phase control on an AC voltage supplied to the lighting load, a switch drive unit for driving the switch unit, and a control unit for controlling the switch drive unit and the control power supply unit.
The control power supply unit is connected to the switch unit in parallel. The control power supply unit converts the AC voltage of the AC power supply into control power. The control power supply unit includes an electrolytic capacitor for storing the control power.
The control unit is supplied with the control power by the control power supply unit via the electrolytic capacitor. The control unit includes a microcomputer. The microcomputer performs an inverse phase control for cutting off, according to the lighting level set by the lighting control operating unit, the supply of the power to the lighting load in the middle of a period set for every half cycle of the AC voltage.
The dimmer of Patent Literature 1 performs cutoff control on the switch unit (bidirectional switch) in the middle of the period set for every half cycle of the AC voltage. That is why cutting off the switch unit during a period with a large current value could have counter electromotive force generated by an inductive component (inductance component) included in the impedance of a line, for example.